Ignition composition



IGNITION COMPOSITION Thomas I. Mulqueeny, Godfrey, and Frederick R.Seavey,

Alton, Ill., assignors to Olin Mathieson Chemical Corporation, acorporation of Virginia No Drawing. Application August 6, 1951 SerialNo. 240,611

6 Claims. (Cl. 52-3) This invention relates generally to electricdetonators or blasting caps, and particularly to the ignition componentof the explosive train therein.

One of the most satisfactorily functioning instantaneous electricdetonators heretofore offered is one wherein a metallic case having anexternal diameter of about .310 inch contains an explosive trainconsisting of: a base charge composed of 4.0 to 4.5 grains of cyclonitepressed into the closed end of the case and overlaid by an initiatingcharge composed of 2.9 to 3.1 grains of lead azide, the latter beingcompressed beneath a protective member which limits the exposure of saidinitiating charge to the superposed ignition charge composed of 4 to 4.5grains of 85% mercury fuhninate-l5% litharge, surrounding a bridge wireof rhodium-rutheniumplatinum alloy of the character disclosed in PatentNo. 2,080,110. While such an electric detonator is somewhat larger thanis desirable for many purposes, it has an advantageously short ignitiontime and total explosion time, and it is relatively insensitive tomechanical shock. When efforts were made to reduce the physicaldimensions of the electric detonator above-described, it was found thatthe detonator became prohibitively sensitive to impact and of erraticperformance when connected in series with other caps of conventionaltype.

The initial objective of the present invention was to reduce thephysical dimensions of the above-described electric detonator withoutsacrificing any of the advantageous characteristics thereof. In thepursuit of such objective, it became a further object to provide anignition composition which, when coordinated with other components,would permit such reduction of size without sacrificing any advantage.The ignition composition hereinafter disclosed not only accomplishesthese objectives, but, in addition, and quite unexpectedly, providesfurther advantageous results, among which are an increase in the numberof caps which can be fired in series without misfires, and animprovement in the constancy of ignition time and in resistance tomechanical impact, adverse storage, and rough handling. The ignitioncomposition contemplated by the present invention is composed of mercuryfulminate and comminuted dense smokeless powder in the proportions offrom 1 to 2.3 parts by weight of the smokeless powder to each part ofmercury fulminate. By dense smokeless powder is meant a smokeless powderbase which has been colloided by means of a solvent or plasticizer,shaped and hardened. An example of dense smokeless powder eminentlysuitable for use in accordance with the present invention is cannonpowder having a chemical composition substantially as follows:

V 2,825,639 Patented Mar. 4,. 1958 Percent On 60 mesh None On 80 m sh 10On 100 m h 50 Through 200 mesh 25-55 A typical screen analysis of themercury fulminate is as followsr.

- Percent On 100 mesh--- 0.5 Through 200 mesh 70 The ground cannonpowder and mercury fulminate are mixed dry in proportions such as toprovide a mixture containing, by weight, between 50% and 70% groundcannon powder with from 50% to mercury fulminate. As the mercuryfulminate approaches the lower limit, the ignition time and totalexplosion time are increased so that, with a mercury fulminate contentof less than 30%, the firing time of the mixture is undesirably long. Asthe content of mercury fulminate approaches 50%, the firing times areshortened, but the difference between the firing times at mercuryfulminate and mercury fulminate is too slight to justify the economicdisadvantage of the greater mercury fulminate content. From thestandpoint of both performance and economics, mixtures containing aboutground cannon powder, with about 40% mercury fulminate, are preferable.

So long as the ground cannon powder has a fineness such as to pass an-mesh screen, it is of no great significance whether the fines bescreened out. This is particularly true of the 60/40 mixture of groundcannon powder and mercury fulminate, and of mixtures within +5% or -5%thereof.

As specific examples of ignition mixtures compounded in accordance withthe present invention, the ground cannon powder may have the compositionindicated under A and B, respectively, in the following table:

3.17 2. 36 Moisture and volatiles -.do- 2. 23 1.62 Ether extractables-do. 0. 8 1. 07 Nitrogen content of nitrocellulose -.do 12.18 12. 50Gravimetric density 400 420 Mercury fulminate was mixed with powders Aand B, respectively, in the proportions of 50/50, 40/60, and 30/70, andthe respective mixtures charged as a loose ignition mixture in electricdetonators having a metallic case whose internal diameter was 0.256inch, with a base charge consisting of 4 /2 grains of cyclonite pressedinto the end of the case, and an initiating charge consisting of 3grains of lead azide pressed on the base charge. The ignition mixturewas charged in a volume sufiicient to substantially fill the spacebetween the initiating charge and the conventionalbridge-wire-supporting plug, so that the ignition charge thoroughlysurrounded the bridge wire. The weight of the ignition charge variedbetween 1.7 and 2.1 grains.

The series of caps containing the several ignition mixtures were testedfor impact sensitivity by being subjected to the blow of a 10-poundweight dropped six feet onto the loaded caps in the axial position, anddropped four 50/50 Mix 40/60 Mix 30/70 Mix Ignition Total Ignition TotalIgnition Total Avg 3. 6 10. 9 3. 9 13.2 5. 3 18. Max 4. 12. 4 4. 5 17. 49.0 20. 1 Min 2. 5 9. 9 3. 0 11. 8 3. 5 16. 4

Neither storage at 130 F. for one Week, nor storage at -40 F. for oneweek, nor storage at 85% relative humidity and 122 F. for thirty days,nor shaking for eight hours on a standard shell shaker, had anysubstantial adverse effect upon either the impact sensitivity or thefiring times of such shells.

An important advantage of blasting caps provided with ignition mixturesin accordance with the present invention, over the instantaneous largersize cap first abovementioned, lies in the increase in the number ofcaps which may be dependably fired in series. The standard series firingtest involves connecting a given number of caps in series and firingthem to ascertain the maximum number which can be so connected andenergized in three consecutive tries without a misfire. On tests madewith a conventional 10-cap blaster, the best results obtainable were 52before shaking and 50 after shaking, with the prior art capabove-described. With caps of the present invention, containing the40/60 ignition mixture, 69 caps were successfully fired in series, bothbefore and after shaking, when compounded with powder A; and 69 and 65,respectively, before and after shaking, when compounded with powder B.

From the foregoing description, those skilled in the art should readilyunderstand the advantages which inhere in the use of an ignition mixturecomposed of comminuted dense smokeless powder and mercury fulminate. Thespecific scientific explanation of the improved performance in theseveral respects above-indicated is not yet ascertained with certainty.

While several specific examples of the ignition composition have beendelineated hereinbefore and alterna- L- tives indicated, it is to bedistinctly understood that the invention is not "limited to the preciseproportions or to the specific compositions of dense smokeless powdershereinbefore specified save as indicated in the appended claims.

Having thus described the invention, what is claimed and desired to besecured by Letters Patent is:

1. In an electric detonator having a base charge and 4 an ignitioncharge, said ignition charge comprising mercury fulminate mixed withground dense smokeless powder in the proportions of from 1.0 to 2.3parts by weight of the powder to each part of mercury fulminate. 2. Theimprovement of claim 1 wherein the powder has a fineness such as to passa 60-mesh screen, and the fulminate has a fineness such that 40-90%passes a 200- mesh screen.

3. The improvement of claim 1 wherein the powder is composedsubstantially as follows:

Percent Diphenylamine .3 to 1.2 Graphite Max. 5.0 Ash. Max 3.0 Moistureand volatiles Max. 2.0 Ether extractables Max 2.75 Nitrocellulose (12.0to 12.7% N) Balance 4. An ignition composition for detonators andblasting caps comprising mercury fulminate mixed with ground densesmokeless powder wherein the mercury fulminate constitutes about 40% byweight of the mixture.

5. In an explosive train for detonators and blasting caps having acyclonite base charge, a lead azide initiating the charge, and anignition charge, the improvement which comprises, said ignition chargebeing composed of -30% loose dry mercury fulminate mixed with 50%70%ground dense smokeless powder, said initiating charge being interposedbetween the ignition charge and the base charge.

6. A composition of matter suitable for use as the ignition charge inelectric detonators consisting of a mixture of mercury fulminate andground dense smokeless powder in the proportions of from 1.0 to 2.3parts by weight of the powder to each part of mercury fulminate.

References Cited in the file of this patent UNITED STATES PATENTS233,406 Faure et al. Oct. 19, 1880 1,481,361 Grotta Jan. 22, 19241,518,629 Woodbury Dec. 9, 1924 2,350,172 Lawrence May 30, 19442,425,854 Alexander Aug. 19, 1947 2,495,868 Power Jan. 31, 19502,511,669 Filbert June 13, 1950 2,607,672 Spaeth et al Aug. 19, 1952FOREIGN PATENTS 198 Great Britain Jan. 15, 1877 of 1877 145,791 GreatBritain May 17, 1921 OTHER REFERENCES Bernadou: Smokeless Powder,Nitrocellulose and Theory of the Cellulose Molecule, pp. 161-164 (1901);pub. by John Wiley & Sons, New York, N. Y.

1. IN AN ELECTRIC DETONATOR HAVING A BASE CHARGE AND AN IGNITION CHARGE,SAID IGNITION CHARGE COMPRISING MERCURY FULMINATE MIXED WITH GROUNDDENSE SMOKELESS POWDER IN THE PROPORTIONS OF FROM 1.0 TO 2.3 PARTS BYWEIGHT OF THE POWDER TO EACH PART OF MERCURY FULMINATE.